With the development of an audio signal coding/decoding technology, more and more electronic equipments transmitting data via an audio interface are produced. For example, the electronic equipment may be connected with a mobile communication device via a low-resistance voice coil type of loudspeaker interface (such as a headphone interface) of the mobile communication device (such as a mobile phone) for receiving an audio signal output from the mobile communication device.
As an output power of the low-resistance voice coil type of loudspeaker interface is usually very low, except the electronic equipment (such as a headphone) with low power consumption, the electronic equipment receiving the audio signal via the low-resistance voice coil type of loudspeaker interface generally needs to use an external power source or an internal battery for normal working, which increases a cost of the electronic equipment and enlarges a volume of the electronic equipment.
For solving the above problems, the inventors propose an audio signal adapter device (such as an audio cable) having a power supplying function, such that the audio signal adapter device can supply power to an audio signal receiving device at the same time when sending an audio signal to the audio signal receiving device.
FIG. 1 is a schematic diagram of an audio cable having a power supplying function. As shown in FIG. 1, the audio cable comprises: a loudspeaker interface (a headphone plug as shown in FIG. 1), a boosting unit (a boosting transformer as shown in FIG. 1), a rectifying unit (a rectifier as shown in FIG. 1), a filtering unit, and a USB plug.
The headphone plug is configured to be connected with a headphone jack of the audio signal sending device (such as the mobile phone), and to receive the audio signal output from the audio signal sending device.
The headphone plug comprises a left-channel pin, a right-channel pin, a ground pin, and a MIC pin.
The left-channel pin and the right-channel pin of the headphone plug are connected with one pin of a primary coil of the boosting transformer, and the ground pin of the headphone plug is connected with the other pin of the primary coil of the boosting transformer.
Furthermore, the ground pin of the headphone plug is further connected with a D− pin of the USB plug.
The boosting transformer comprises the primary coil and a secondary coil, and is configured to raise an input voltage (commonly about 1V) at an input end (the primary coil) to an output voltage (for example, larger than or equal to 5V) at an output end (the secondary coil).
As described above, the primary coil of the boosting transformer has two pins, one pin is connected with the left-channel pin and the right-channel pin of the headphone plug respectively, and the other pin is connected with the ground pin of the headphone plug.
The output coil of the boosting transformer has two output pins and one tap, the two output pins are connected with two input pins of an input end of the rectifier respectively, and the tap is connected with the ground pin of the USB plug.
The rectifier is configured to rectify an alternating current level input from the input end thereof, and to output the rectified level via an output end thereof.
The rectifier has two input pins of the input end, and one output pin of the output end; accordingly, the rectifier comprises two diodes, positive poles of the two diodes are connected with the two input pins of the rectifier respectively, and negative poles of the two diodes are connected with the output pin of the rectifier.
The filtering unit has an input end and an output end, and is configured to convert a level input from the input end to a smooth direct current level, and to output the smooth direct current level via the output end.
The input end of the filtering unit is connected with the output end of the rectifier, and the output end of the filtering unit is connected with a VBUS pin (a power pin) of the USB plug, via which a power is supplied to the audio signal receiving device connected with the USB plug.
The input end and the output end of the filtering unit are connected, and the filtering unit comprises a capacitor C1, one end of which is connected with the input/output end of the filtering unit, and the other end of which is connected with the ground pin of the USB plug.
Furthermore, the left-channel pin and the right-channel pin of the headphone plug are further connected with a D+ pin of the USB plug.
When the audio cable shown in FIG. 1 is connected with the electronic equipment, the headphone plug of the audio cable is plugged into the headphone jack of the audio signal sending device (such as the mobile phone), and the USB plug of the audio cable is plugged into the USB slot of the electronic equipment. Such that, the audio signal receiving device gains power via the VBUS pin of the USB socket/slot, meanwhile, uses the D+ pin as an audio signal pin and uses the D− pin as a reference signal pin, so as to receive the audio signal output from the headphone jack of the audio signal sending device.
Furthermore, the structure of the audio cable shown in FIG. 1 may have a variety of variations as follows.
(1) using the D− pin of the USB socket as the audio signal pin, and using the D+ pin as the reference signal pin;
(2) connecting only one audio pin (such as the left-channel pin) of the headphone plug with the primary coil of the boosting transformer, and connecting the other audio pin (such as the right-channel pin) with the D+ pin only.
As described above, the audio cable shown in FIG. 1 can realize an adapter function between the headphone interface and the USB interface, and realize supplying power to the audio signal receiving device via the VBUS pin and the ground pin of the USB interface end (the USB plug).
However, when the audio cable shown in FIG. 1 is used, as the ground pin of the USB interface is occupied and the D+ pin and the D− pin are used as the audio signal pin and the reference signal pin of the audio signal receiving device respectively for receiving the audio signal, the MIC pin of the headphone plug cannot be connected with the audio signal receiving device, which makes the audio signal receiving device unable to send a signal to the audio signal sending device.